Netiquette

Use of Capitals and lower case letters
You capitalize letters at the beginning of each sentence, a persons name, the name of something "important", if you want something to stand out (where possible), etc.
You use lower case letters for most words in the body of your sentence. Not unless they pertain to the information above, they are lower case. Don't use all caps because it looks like you are showing too much emotion or are yelling. You don't want to offend your audience.

Subject Lines
Subject lines in emails, memos, etc. should be brief and concise. They should be able to give the reader the main idea of the letter without ever having to read it first. Most be relatively close to what the message is about, because that could be the difference from someone reading it and someone putting it in the trash.

Timeliness of replies
The response at which you reply something allows the sender to know you are actively engaged in your work and that you care about your job or the sender's feelings. The rate at which you reply to something shows the sender about your character and what kind of person you are. A response that is long after the message has been sent, shows the reader either doesn't care or is just to busy to help the sender out. Not what bosses at businesses want to see.

References:
http://www.livinginternet.com/i/ia_nq.htm